1. Field of the Invention
The present invention relates to a dispersion composition comprising a functional substance and a polymer, which can be used as various functional materials. This invention also relates to an ink composition, a method of forming an image and an image forming apparatus using the same. In particular, the present invention relates to an ink composition which is an image forming material that can be preferably used for a printer or a display, wherein the dispersion composition containing a functional substance is an aqueous dispersion material, a method of forming an image and an image forming apparatus using the same.
2. Related Background Art
Dispersion compositions that contain functional materials have been widely used for agricultural chemicals such as pesticides and insecticides and pharmaceuticals such as antitumor agents, antiallergic agents and antiinflammatory agents. In addition, coloring materials which contain a coloring agent as the functional material, such as ink and toner, are known. Recently, digital printing technology has been developing at a remarkable speed. This technology, represented by electrophotography and ink jet technology, is now becoming more and more important in office and home as an image forming technology.
Of these technologies, the ink jet technology employs a direct printing method, and its major characteristics include compact size and low power consumption. Further, as the nozzles have become finer, higher image quality has been achieved. An example of ink jet technique is a method where ink supplied from an ink tank is heated by a heater provided in a nozzle to form a bubble therein, whereby the ink is ejected to form an image on a recording medium. Another method is ejecting ink from a nozzle by vibrating a piezo-electric device.
Since the ink used in these ink jet methods is usually an aqueous dye solution, blurring may occur when colors are superimposed and a phenomenon called feathering may occur at the printed area of the recording medium along the fibers of paper. To improve this situation, use of pigment dispersion ink has been studied. For example, according to one method, a pigment is dispersed by an ionic block polymer containing at least one hydrophilic component and at least one hydrophobic component (U.S. Pat. No. 5,085,698). However, further improvement is desired in stable and long term dispersion in a solvent by suppressing aggregation due to interaction between particles, as well as in color and color development.